With the increased speed and greater size of land transportation machinery such as railroad cars and automobiles, as well as motor bicycles and the like, disc brakes have come to be widely used as braking devices for such vehicles.
Following is a description of an example of a disc brake used for a railroad car.
A disc braking system operates a brake caliper which presses a brake lining on a sliding surface of a brake disc mounted onto an axle or a wheel so as to produce a braking force and thereby control the speed of a vehicle by damping the rotation of the axle or the wheel.
When it works, the temperature of a contact surface of the brake lining and the brake disc rises due to a frictional heat, and with an increasing speed of the vehicle, the temperature of the contact surface rises due to an increased brake load.
In a conventional disc brake of the type shown in FIG. 6, a brake lining 1 has a structure such that a friction member 1a, which makes contact with a sliding surface 2a of a brake disc 2, is attached to a back plate 1b by means of a rivet (not pictured) or an adhesive or the like.
A pressing force which is applied as a load by the brake caliper onto the brake lining does not operate evenly on the entire brake lining, but rather, it concentrates on a specified area thereof, due to the structure of an attaching member. For example, in the case of a hydraulic caliper, a central position 3 of a pressing load is located on a compressing piston, as shown in FIG. 6. In the case of a lever caliper, a pressing load is applied at a location where a caliper arm and a lining holder interface with each other, in a similar manner as in the case of the hydraulic caliper.
As described above, the conventional disc brake has a structure such that the pressing force applied by the brake caliper operates only on a portion of the brake lining. As a consequence, the contact surface pressure between the brake lining and brake disc increases directly beneath the location where the pressing force operates, producing a local rise in temperature.
Accordingly, a uniform surface pressure lining is needed to mitigate the local rise in temperature. For example, Patent Reference 1 discloses a brake lining with a friction member 11 attached to a back plate 12, with an elastic member 13 disposed between them, and arranged so as to avoid a fastening hole 21, as shown in FIG. 7. Provision of such a structure equalizes the contact surface pressure between the brake lining and the brake disc, and inhibits the local temperature from rising.
However, the technology disclosed in Patent Reference 1 interposes an elastic member when attaching a the friction member to the back plate, so that when a pressing force operates, the friction member increases in temperature, and the elastic member yields, subsequently making it impossible for the elastic member to effectively achieve its inherent uniform surface pressure function.
In Patent References 2 and 3, technologies are disclosed for uniformly applying the pressing force from the brake caliper and inhibiting the local temperature from rising, by dividing the friction member into a plurality of parts with spherical-seated structure disposed between them.
However, in the technologies disclosed in Patent References 2 and 3, the uniform surface pressure function is lost if the components of the spherical-seated structure undergo plastic deformation due to the pressing force.